Discussion of Background
Conventionally, the labels used in the cosmetics field are formed from self-adhesive sheets made of materials such as high-density polyethylenes, polypropylenes, polyvinyl chlorides, polyethylene terephthalates, or paper. The face of the sheet on the opposite side from the adhesive layer is printed, such as by screen printing, typography, flexography, photogravure or offset printing. A lacquer is optionally deposited on the printed face and dried, conventionally or by ultraviolet radiation.
Generally, in the labeling field, the labels are placed on at least one of the faces of a support tape wound around a core. The support is continuously fed to a labeling station at which the labels are transferred onto objects to be labeled. On leaving the labeling station, the support is wound around a spindle, and scrapped or recycled.
Supports provided with labels on both their faces are also known. These can be used for feeding continuous labeling chains as described in documents FR-A-2 789 971 and FR-A-2 789 972. These two-sided label supports have the advantage of minimizing the amount of support tape to be subsequently scrapped or recycled once all the labels have been removed.
Supports provided with labels made of polyethylene, the thickness of the labels of which is around 80 to 100 μm, are known.
Also known from the prior art are thin labels made of polyethylene terephthalate that are bonded by means of an adhesive layer to both faces of a paper support or a support made of a thermoplastic. The faces of the support are preferably siliconized in order to facilitate the detachment of the labels coated with their adhesive by the labeling stations. The thickness of such a support provided with labels on both its faces is known to be around 60 to 150 μm.
The advantage of polyethylene terephthalate labels is the ability to obviate treatments prior to the printing, of the corona or “top coating” type, that are used to improve the printability and the retention of the ink on the upper surface of the label. This is because polyethylene terephthalate already allows, without any specific treatment, more optimum and durable printability.
The problem posed by the two-sided supports of the prior art is that they are too thick when they have polyethylene labels and they are expensive to produce when they have polyethylene terephthalate labels. The recycling of polyethylene terephthalate is also generally more expensive than the recycling of other thermoplastics.
Finally, the inventor is aware that the problems associated with the high level of products deemed to be defective on leaving the labeling station, and the problems of the labeling stations slowing down or becoming blocked, can be due to the electrostatic potential developed by these polyethylene terephthalate labels. Thus, when the labeling station unwinds the support, it may turn out that the electrostatic potential of the labels is sufficient to generate a static electricity spark on passing through the labeling station. This spark can result in the ignition of the support or the labels. Such ignition then makes, respectively, the labels and the support unsuitable for use. The labeling station therefore has to be stopped.
Even if the label passes through the labeling station without creating sparks, since the label still has a high electrostatic potential when it is mechanically presented against the object onto which it has to be bonded, it can be repelled by the object. A first risk is that the label will completely fail to be bonded to the product. A second risk is that the label will be bonded to the object in an offset manner. In the latter case, the label will not be at an expected place on the object. In both situations, the resulting objects can be considered defective and unsuitable for sale as such. It will therefore be necessary for these objects to be removed manually, and the production costs will thereby be increased.
The existence of such an electrostatic field may also block the upstream labeling station. This is because the electrostatic field created between two labels facing each other may even be higher than the adhesive force conferred by the adhesive that keeps the labels on their support. Consequently, a label may become prematurely separated from its support—it is then free and can “fly” in the labeling station. There is therefore a risk of it disturbing or even blocking or jamming the labeling chain, and time will then be unnecessarily wasted in getting the labeling machine back into operation.